When a vehicle is launched the engine is typically engaged with and disengaged from the transmission via a clutch. The clutch includes a disc with a friction coating that is engaged with a flywheel. When the clutch is engaged against the flywheel, the clutch slips for some period of time before engaging or locking against the flywheel. Once engaged, the vehicle may be accelerated by depressing the accelerator and subsequently shifting up through the gears.
In some applications, the vehicle may be caused to stall if the accelerator is not depressed (causing the engine to produce additional torque and engine speed to increase). For instance, automobiles with manual clutches may stall if the clutch is simply released without affecting the accelerator. On the other hand, if the accelerator is depressed too much, a significant amount of clutch slippage can occur, which leads eventually to failure of the clutch.
Heavy and medium duty trucks with their corresponding engines, however, typically generate considerably more torque than that found in consumer-based automotive applications. Thus, in such a vehicle, a manually operated clutch can be slowly released without touching the throttle pedal. An engine idle governor may be used to prevent the engine from stalling by providing additional fuel near the engine idle speed as the clutch closes. This puts minimal energy into the clutch, allowing the clutch to remain as cool as possible and extending clutch life.
Some heavy duty and medium duty vehicles include an Automated Manual Transmission (AMT). In an AMT, the transmission base box is similar to that used in a manual transmission. However, instead of a shift handle, gear selection is automated. Automation could be provided by a pair of electric motors (sometimes referred to as an XY shifter). Further, it is contemplated that there are other methods of shifting besides a set of electric motors, and the XY is one example but an AMT could have another actuation device, including pneumatic devices). Launching a heavy duty or medium duty vehicle using an AMT has many similarities to a similar vehicle with a manual transmission. To maximize clutch life, low engine speeds are used when launching the vehicle. To avoid stalling, though, a transmission controller selects a target engine speed (called the reference speed) for launching the vehicle. A typical reference speed may be 1000 rpm, as compared to a typical idle speed of 700 rpm. A target engine speed for launch may be, in one example such as in a heavy truck application, 300 rpm greater than the idle speed.
In some instances, fleets of heavier duty non-automotive vehicles may be deployed having AMTs. The AMTs are generally preferred to improve clutch life while also improving fuel efficiency. That is, although the engine may not produce peak torque at idle, for a typical launch the amount of torque generated is sufficient to move the vehicle forward from a stopped position. However, inevitably some of the vehicles encounter obstacles that cause resistance to wheel rotation, which may include curbs, deep ruts, and the like. Thus, vehicles having an AMT may struggle, as the engine speed, and therefore the available torque, is low during launch and the target engine speed may provide inadequate available torque when encountering the above obstacles.
Therefore, it is desirable to improve transmission operation of heavier duty non-automotive vehicles having AMTs by controlling events that cause excessive wear to the clutch.